Service Providers and Related Party Agreements - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Related Party Transactions [Abstract]
Management fee percentage per annum of daily NAV			0.85%
Managing owner waived fees	$ 107,259	$ 135,535	$ 219,832	$ 229,185